An analog-digital-converter (ADC) is employed to change/convert an analog input signal into a digital output signal. There are several different types of ADC architectures in current use, including pipeline, flash and folding. In a flash ADC, k bits of resolution employ 2k comparators to convert an analog signal into a digital signal. Folding ADCs are a variation of a typical flash ADC architecture except that they are arranged to map the analog input signal range into N regions where each of these N regions share the same comparators. In a folding ADC, the total number of comparators is typically 2k/N+(N−2).
Flash and folding ADCs may be scaled to very high conversion speeds, since they do not use decision feed-back loops. These two architectures, unfortunately, can be sensitive to device mismatch, leading to linearity degradation. This is especially true of CMOS folding ADCs, since CMOS devices have larger offsets than bipolar devices.
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